1. Field of the Invention
The present invention relates to an image decoding apparatus, an image decoding method and a computer program. More specifically, the present invention relates to an image decoding apparatus, an image decoding method and a computer program that utilize a correction value table where a correction value, previously prepared by statistically processing a coefficient value truncated by a bit-plane truncation, is stored for every bit-plane truncation position, and that stably suppress a sense of incongruity or a sense of confusion occurring in a reproduced image by executing correction on the transform coefficient obtained by performing a decoding process on an encoded stream using the correction value, corresponding to the bit-plane truncation position, read from the correction value table.
2. Description of the Related Art
One of the typical image compression schemes according to the related art is, for example, the JPEG (Joint Photographic Experts Group) scheme standardized by the ISO (International Standards Organization). This scheme utilizes discrete cosine transform (DCT). When a relatively high bit is assigned, it has been shown that excellent encoded and decoded images are obtained. Recently, wavelet transform encoding has been used in which an image is divided into a plurality of bands by a filter that is a combination of a high-pass filter and a low-pass filter, called a filter bank, and encoding is performed for each band. The wavelet transform encoding has been considered as new prevailing technology which will take over from DCT because the wavelet transform encoding does not have the drawback of block distortion conspicuously appearing with high compression as in DCT.
The JPEG-2000 scheme has been standardized as an image compression scheme using such wavelet transform encoding. The JPEG-2000 scheme is a scheme that is a combination of the wavelet transform and bit-plane encoding, and realizes great improvement in encoding efficiency as compared with JPEG.
In addition, Japanese Unexamined Patent Application Publication No 2002-165098 discloses that rate control is made possible by performing a bit-plane truncation process for truncating a generated encoded stream data from the tail end thereof, in order to be capable of obtaining a target amount of code when using the JPEG-2000 scheme. Meanwhile, Japanese Unexamined Patent Application Publication No 2004-260539 discloses that it is performed to suppress a sense of incongruity or a sense of confusion occurring in a reproduced image by generating random numbers expressible by the number of truncated bits and adding the random numbers to a wavelet coefficient, when decoding is performed using the encoded stream data on which the bit-plane truncation has been performed. In addition, Japanese Unexamined Patent Application Publication No 2002-204357 discloses that as replacement of the signal component lost in the irreversible compression process, noise is included in decoded image data as a pseudo signal to thereby make improvements in deterioration of an image quality due to signal loss at the time of encoding. In addition, it is also performed to use substantially central values of values expressible by the number of truncated bits as values shown by the truncated bits.